Favorable remodeling enhances recovery of regional myocardial function in the weeks after infarction in ischemically preconditioned hearts

Background-In a previous study, we found that recovery of segment shortenin g in the ischemic zone of conscious, chronically instrumented rabbits was s ignificantly better in ischemically preconditioned than control animals aft er 72 hours of reperfusion. However, although this period of reperfusion wa s felt to be sufficient to allow recovery from stunning, regional function was disproportionately low for the size of the infarcts, Methods and Results-To further characterize the recovery of left ventricula r regional function, rabbits were chronically instrumented with a balloon o ccluder around a branch of the left coronary artery and a pair of ultrasoni c crystals to monitor segment shortening in the ischemic zone. The precondi tioned group had 1 cycle of 5-minute occlusion/10-minute reperfusion before a 30-minute occlusion, whereas control rabbits experienced only the 30-min ute occlusion. All monitored segments were either dyskinetic or akinetic du ring the 30-minute occlusion. There was no difference in function between t he 2 groups until 24 hours of reperfusion. At 72 hours, systolic shortening in control hearts averaged only 5% of the preischemic value, whereas short ening was 29% of baseline in preconditioned hearts. By day 21, systolic sho rtening averaged 26% in control hearts and 65% in preconditioned hearts (P< 0.02) and appeared to have reached a plateau. Infarct size was 31.4+/-2.8% and 15.5+/-2.1% in control and preconditioned hearts, respectively. Moreove r, in ischemically preconditioned hearts, the recovery of regional function was better than in controls for any given amount of microinfarction in the myocardial segment between crystals (P=0.02). Conclusions-The progressive improvement in preconditioned hearts is most co nsistent with favorable remodeling in the ischemic zone, which the precondi tioning process seems to accentuate.